The present invention relates to a micromechanical angular-acceleration sensor.
Rpm sensors (gyroscopes, rotational speed sensors) are usually used to determine angular acceleration. In this case, the angular acceleration is derived from the yaw rate (rate of rotation) by differentiating it with respect to time.
Rpm sensors usually requiring relatively complicated evaluating electronics are discussed in M. Lutz, W. Golderer, J. Gerstenmeier, J. Marek, B. Maihxc3x6fer, and D. Schubert, A Precision Yaw Rate Sensor in Silicon Micromachining, SAE Technical Paper, 980267; and from K. Funk, A. Schilp, M. Offenberg, B. Elsner, F. Larmer, Surface-micromachining of Resonant Silicon Structures, The 8th International Conference on Solid-State Sensors and Actuators, Eurosensors IX, Stockholm, Sweden, Jun. 25-29, 1995, pages 50-52.
In addition, an angular-acceleration detection system is disclosed in German Patent No. 196 323 63, where several acceleration sensors are evaluated electronically, and the angular acceleration is derived by combining, i.e. forming the differential, cumulative, and average values of, the acceleration-sensor signals.
Furthermore, Mizuno J., Nottmeyer K., Kanai Y., Berberig O., Kobayashi T., Esashi M., Proc. Transducers xe2x80x299, Sendai, Japan, June 7-10, 1999, pages 1302-1305, describes a complicated, combined linear/angular-acceleration sensor.
Therefore, the present invention is based on the general problem of providing a micromechanical angular-acceleration sensor, which requires relatively simple evaluating electronics.
The present invention is based on the idea of being able to determine the angular acceleration without the time derivative of the rotational speed, by using certain sensor patterns. For this purpose, a simple, capacitive, differential-capacitance measuring set-up can be used.
The micromechanical angular-acceleration sensor, which is in accordance with the present invention, has the particular advantage of being small in size and, for example, being able to be manufactured inexpensively, using a standard, surface-micromechanics manufacturing method.
The series production method is a method that is also known from the manufacture of acceleration sensors having comb patterns. The use of surface micromechanics, especially the serial production method having a thick epipoly layer that is typically 10 xcexcm thick, permits the production of a stiff sensor structure, which allows a small lateral sensitivity to be attained.
A further refinement provides a deflectable, third capacitor-plate device attached to the ring-shaped centrifugal mass, and a stationary, fourth capacitor plate device attached to the substrate. The third and fourth capacitor-plate devices are designed as a stiffness-tuning device for electrostatically tuning the spring constant of the torsion spring. This allows the measuring sensitivity to be adjusted beyond the technical limits of the method.
According to an additional refinement, the centrifugal mass has an annular structure and can be deflected about the rotational axis normal to the surface of the substrate.
In another refinement, the first capacitor plate device and the third capacitor plate device are formed in recesses of the annular structure. This saves valuable layout space.
A further refinement has the second capacitor plate device and fourth capacitor plate device extending into the recesses of the annular structure. This provides a compromise between a mass which is far away from the point of rotation (maximum moment of inertia) and electrodes which are also located far out for converting the angular change caused by an external angular acceleration into a change in distance that is as large as possible.
According to another refinement, the centrifugal mass has a double-ring structure, and can be displaced about a rotational axis normal to the substrate surface. In this case, the differential-capacitor device and/or the stiffness-tuning device are expediently arranged between the two circular rings.
According to a further refinement, the torsion spring device is led through breaks in the inner circular ring to the outer circular ring. This reduces the flexural stiffness, and therefore increases the sensitivity.
According to another refinement, the centrifugal mass has a rectangular-ring structure and can be displaced about a rotational axis running in a direction parallel to the substrate surface. This also yields a rotationally symmetric centrifugal-mass structure for this rotational axis.
An additional refinement provides for the first capacitor-plate device being on the sides of the rectangle that run in a direction parallel to the rotational axis, and for the second capacitor-plate device being in substrate regions subjacent thereto. This allows a differential capacitor to be produced according to the rocker principle.